This invention relates generally to disk drive systems for storing digital data and more particularly to such systems utilizing servo information recorded on a disk surface for controlling the positioning of read and/or write heads with respect to a plurality of concentric tracks recorded on other disk surfaces.
Typical high capacity disk storage systems use a plurality of rigid magnetic disks stacked on a common spindle. For example only, such a system may consist of five disks defining ten major disk surfaces with one surface being dedicated to storing servo information and nine surfaces (typically, only eight are used) for storing digital data. Such a disk system typically includes a positioner subsystem, mounted adjacent to the disk stack, carrying a plurality of aligned read/write heads including at least one head per active disk surface (i.e. servo plus data surfaces). The heads are typically mounted on a common head arm which is coupled to a positioner motor. Energization of the positioner motor moves the arm to thus move each head radially relative to its disk surface. By properly controlling the positioner motor, the heads can seek, and then follow, any selected one of a plurality of concentric tracks.
A disk storage system is typically comprised of two primary portions; namely, a head disk assembly (HDA) and a controller electronics board. In the normal operation of such a system, a track seek command is issued by a host computer to the controller electronics via an appropriate interface board. The controller electronics determines the direction and magnitude of movement required to move the heads from their current track (or "cylinder") position to the new or destination track. Based on this information, the controller electronics selects an optimized velocity profile to rapidly move the head arm to position the heads over the destination track.
High performance disk storage systems attempt to maximize the density at which tracks are written on the disk surface. For example, it is not unusual for such systems to record tracks at a density in excess of one thousand per radial inch. In order to achieve such high track densities and permit rapid head positioning, the positioner motor is usually operated in a closed servo loop. That is, as the positioner motor is energized to move the heads, the head associated with the dedicated servo surface counts track crossings of a prerecorded servo pattern until the head arrives at its destination track. More specifically, assume for example that the heads are currently at track 19 and that the computer issues a command to move the heads to track 739. In response, a track counter is set to the magnitude of movement required, i.e. 720, and the positioner motor is moved in accordance with a velocity profile which permits it to accelerate to a maximum velocity, maintain that maximum velocity for a certain interval, and then decelerate to reach zero velocity concurrent with the head arriving at the destination track. The velocity transition points are generally determined by the current count in the track counter which is decremented as the servo head detects each track crossing of the servo pattern recorded on the dedicated servo surface.
The foregoing explanation generally describes various state of the art systems well known in the literature and widely commercially available. Such systems differ in many specific aspects including the electromechanical design of the HDA, the particular servo pattern employed on the disk surface, the electronic design of the controller electronics, etc. In all such systems, however, it is necessary that the servo information be originally recorded, generally during a phase of factory check out, before the system can be operational inasmuch as the servo information is relied on for normal track seeking (counting), track following, and head velocity determination.
The present invention is primarily directed to a method and apparatus for originally recording servo information on a disk surface. Prior techniques for recording servo information at high track densities have generally utilized laser based servo writer assemblies in which the physical position of the servo head is measured at each track by a laser measuring system (e.g. Hewlett-Packard Model 5528A). Such servo writer assemblies are expensive and bulky.